The present invention relates to a resin-molded semiconductor device in which a semiconductor chip and signal-connecting leads to be connected to the chip are encapsulated with a resin encapsulant, a method for manufacturing such a device, and a lead frame suitable for manufacturing the resin-molded semiconductor device. In particular, the present invention relates to an improved device with a reduced thickness.
In recent years, in order to catch up with rapidly advancing downsizing of electronic appliances, it has become increasingly necessary to mount semiconductor components with higher and higher density. Correspondingly, sizes and thicknesses of semiconductor components have also been noticeably reduced.
Hereinafter, a conventional resin-molded semiconductor device will be described.
FIG. 20 is a cross-sectional view of a conventional resin-molded semiconductor device. As shown in FIG. 20, this semiconductor device includes external electrodes on its back surface.
The semiconductor device further includes a lead frame consisting of: inner leads 101; a die pad 102; and support leads (not shown) for supporting the die pad 102. A semiconductor chip 104 is bonded onto the die pad 102 with an adhesive, and electrode pads (not shown) of the chip 104 are electrically connected to the inner leads 101 with metal fine wires 105. And the die pad 102, semiconductor chip 104, part of the inner leads 101, support leads and metal fine wires 105 are encapsulated with a resin encapsulant 106. In this structure, no resin encapsulant 106 exists on the back surface of the inner leads 101. In other words, the respective back surfaces of the inner leads 101 are exposed and the respective lower parts of the inner leads 101, including the exposed back surfaces thereof, are used as external electrodes 107. To improve the adhesion between the resin encapsulant 106 and the inner leads 101 or the die pad 102, the side faces of the leads 101 and the pad 102 are formed like a taper with an upwardly increasing thickness, not to extend perpendicularly to their upper and lower surfaces.
In such a resin-molded semiconductor device, the respective back surfaces of the resin encapsulant 106 and the die pad 102 are both located on the same plane. Stated otherwise, the back surface of the lead frame is not substantially encapsulated. Accordingly, the thickness of such a semiconductor device is thinner than usual.
A resin-molded semiconductor device having such a structure as that shown in FIG. 20 is manufactured in the following manner. First, a lead frame including inner leads 101 and a die pad 102 is prepared and then wrought mechanically or chemically to shape the side faces of the lead frame like a taper. Next, a semiconductor chip 104 is bonded onto the die pad 102 of the lead frame prepared, and is electrically connected to the inner leads 101 with metal fine wires 105. As the metal fine wires 105, aluminum (Al) or gold (Au) wires may be appropriately used, for example. Then, the die pad 102, semiconductor chip 104, inner leads 101, support leads and metal fine wires 105 are encapsulated with a resin encapsulant 106. In this case, the lead frame, on which the semiconductor chip 104 has been bonded, is introduced into a die assembly and transfer-molded. In particular, resin molding is performed with the back surface of the lead frame in contact with an upper or lower die of the die assembly. Finally, parts of outer leads, protruding outward from the resin encapsulant 106, are cut off, thereby completing a resin-molded semiconductor device.
Although a conventional resin-molded semiconductor device of this type has a reduced thickness, the device has the following problems.
Firstly, a resin encapsulant covers the upper and side faces of a die pad, but does not exist on the back surface thereof. Accordingly, the resin encapsulant cannot hold the die pad and the semiconductor chip so strong as that of other thicker devices, resulting in deterioration in reliability of the device.
Secondly, stress applied by the resin encapsulant or stress applied after assembling might have unwanted effects on a semiconductor chip or the resin encapsulant might possibly crack. Particularly when moisture penetrates between the die pad and the resin encapsulant, the adhesion therebetween decreases to a noticeable degree or considerable cracking is created. As a result, the reliability of the device further deteriorates.
Thirdly, although a resin-molded semiconductor device can be generally mounted accurately on a motherboard to be self-aligned with its desired position using the tension of solder, the time taken to settle the self alignment is still to be shortened and the mounting accuracy is still to be improved.
Fourthly, if part of a resin encapsulant sticks out of the back surface of a die pad in bonding the die pad and a motherboard (i.e., if so-called resin burr exists), then desired characteristics might not be attained in terms of heat radiation, for example. This is because the die pad cannot be in satisfactory contact with a heat-radiating pad in such a case. Such resin burr can be removed by using water jet or the like. However, such a process is not just troublesome, but causes additional problems. Specifically, if a water jet process is carried out, then a nickel, palladium or gold plated layer might peel off and impurity might deposit on the exposed parts. Accordingly, such parts exposed on the resin encapsulant should be plated once again after the encapsulation. As a result, work efficiency and reliability of the device might possibly deteriorate.
A first object of this invention is providing a resin-molded semiconductor device suppressing delamination of a die pad by making a resin encapsulant hold the pad more strongly when the lower surface of the pad is exposed on the encapsulant, and a lead frame suitable for manufacturing such a device.
A second object is providing a resin-molded semiconductor device, preventing a resin encapsulant from cracking due to penetration of water or moisture between a die pad and the encapsulant, and a lead frame suitable for manufacturing such a device.
A third object is providing a resin-molded semiconductor device that can be self-aligned with a desired position on a motherboard more accurately by using a structure where the lower surface of a die pad is exposed on the resin encapsulant, and a method for manufacturing the same.
A fourth object is providing a resin-molded semiconductor device with heat radiation characteristics improved by preventing the formation of resin burr even if the lower surface of a die pad is exposed on the encapsulant, a manufacturing method thereof, and a lead frame suitable for manufacturing such a device.
A fifth object is providing a resin-molded semiconductor device in which solder balls need not be interposed between a die pad and a heat-radiating pad, and a method for manufacturing the same.
A first lead frame according to the present invention includes: an outer frame surrounding a region in which a semiconductor chip is mounted; a die pad formed in the region surrounded by the outer frame; a support portion for supporting the die pad by connecting the die pad to the outer frame; and signal-connecting leads connected to the outer frame. A convex portion protruding downward and a flange portion surrounding the convex portion are formed as lower part of the die pad.
In this structure, even if the lower surface of the convex portion of the die pad is not covered with the resin encapsulant in mounting a semiconductor chip on this lead frame and encapsulating the chip and the lead frame with a resin encapsulant, the encapsulant exists under the flange portion of the die pad. As a result, a resin-molded semiconductor device, where a resin encapsulant can hold the die pad more strongly, is obtained. That is to say, the first object is accomplished. In addition, since the adhesion between the resin encapsulant and the die pad increases in such a structure, penetration of water or moisture through the boundary between the resin encapsulant and the die pad can be suppressed. Consequently, the second object, or increase in moisture resistance, is also achieved.
A second lead frame according to the present invention includes: an outer frame surrounding a region in which a semiconductor chip is mounted; a die pad formed in the region surrounded by the outer frame; a support portion for supporting the die pad by connecting the die pad to the outer frame; and signal-connecting leads connected to the outer frame. The die pad is provided with a hole.
In this structure, when a semiconductor chip is mounted onto this lead frame and the lead frame and chip are encapsulated with a resin encapsulant, the encapsulant also exists inside the hole, thus increasing the force of the encapsulant holding the die pad. Accordingly, the first and second objects are accomplished.
In one embodiment of the present invention, the hole of the die pad has a stepped shape, the lower part of the hole being wider in diameter than the upper part thereof.
In such an embodiment, not only the resin encapsulant can hold the die pad even more strongly, but also the moisture resistance of the device can be remarkably increased.
A third lead frame according to the present invention includes: an outer frame surrounding a region in which a semiconductor chip is mounted; a die pad formed in the region surrounded by the outer frame; support leads for supporting the die pad by connecting the die pad to the outer frame; and signal-connecting leads connected to the outer frame. The die pad is located below the outer frame.
In this structure, when a semiconductor chip is mounted onto this lead frame and the chip and the lead frame are encapsulated with a resin encapsulant, clamping force, applied through a die assembly onto the outer frame, is efficiently applied to the die pad. Thus, if encapsulation is performed with a seal tape adhered to the lower surface of the lead frame, then the die pad is advantageously forced into the seal tape. Accordingly, this lead frame is suitable for protruding the die pad downward from the back surface of the resin encapsulant. In other words, since a standoff height is secured, solder balls or the like no longer need to be interposed between the die pad and a motherboard. As a result, the fifth object is accomplished.
In one embodiment of the present invention, part of each said support lead is bent to function as a spring.
In such an embodiment, since each support lead is deformed at its bent portion, deformation of the die pad due to pressure can be suppressed.
A fourth lead frame according to the present invention includes: an outer frame surrounding a region in which a semiconductor chip is mounted; a die pad formed in the region surrounded by the outer frame; support leads for supporting the die pad by connecting the die pad to the outer frame; and signal-connecting leads connected to the outer frame. The die pad is located below the outer frame, and the support leads are provided between the signal-connecting leads and the die pad.
In this structure, when a semiconductor chip is mounted onto this lead frame and the chip and the lead frame are encapsulated with a resin encapsulant, clamping force, applied through a die assembly onto the outer frame, can be transmitted to the die pad even more efficiently. Thus, the same effects as those of the third lead frame can be attained.
In one embodiment of the present invention, part of each said support lead is bent to function as a spring, and the thickness of the bent part of each said support lead is reduced at the bottom thereof.
In such an embodiment, after a semiconductor chip has been mounted onto this lead frame and the chip and the lead frame have been encapsulated with a resin encapsulant, the signal-connecting leads connected to the support leads can be cut off more easily.
A first resin-molded semiconductor device according to the present invention includes: a semiconductor chip having electrode pads; a die pad for supporting the semiconductor chip thereon; signal-connecting leads; connecting members for electrically connecting the electrode pads of the semiconductor chip to the signal-connecting leads; and a resin encapsulant for encapsulating the die pad, the semiconductor chip, the signal-connecting leads and the connecting members. A convex portion protruding downward and a flange portion surrounding the convex portion are formed as lower part of the die pad. And at least lower part of the convex portion of the die pad is not covered with the resin encapsulant but exposed, whereas the flange portion of the die pad is buried in the resin encapsulant.
In this structure, the resin encapsulant exists under the flange portion of the die pad. Accordingly, the resin encapsulant can hold the die pad more strongly and the first object is accomplished. In addition, since penetration of water or moisture through the back surface of the resin-molded semiconductor device can also be advantageously suppressed as described above, the second object is achieved as well.
A second resin-molded semiconductor device according to the present invention includes: a semiconductor chip having electrode pads; a die pad for supporting the semiconductor chip thereon; signal-connecting leads; connecting members for electrically connecting the electrode pads of the semiconductor chip to the signal-connecting leads; and a resin encapsulant for encapsulating the die pad, the semiconductor chip, the signal-connecting leads and the connecting members. Lower part of the die pad is at least partially not covered with the resin encapsulant but exposed, and the die pad is provided with a hole.
In this structure, since the resin encapsulant exists inside the hole of the die pad, the resin encapsulant can hold the die pad even more strongly. As a result, the first and second objects are accomplished.
In one embodiment of the present invention, lower part of the die pad protrudes at least partially from the resin encapsulant.
In such an embodiment, the resin-molded semiconductor device is obtained by encapsulating the chip and the lead frame, with a seal tape adhered to the lower surface of the die pad, which is forced into the seal tape. Accordingly, in this structure, no resin encapsulant sticks out of the hole on the lower surface of the die pad. As a result, a resin-molded semiconductor device excellent in heat radiating characteristics, where no resin burr exists on the lower surface of the die pad thereof, can be obtained.
A third resin-molded semiconductor device according to the present invention includes: a semiconductor chip having electrode pads; a die pad for supporting the semiconductor chip thereon; signal-connecting leads; connecting members for electrically connecting the electrode pads of the semiconductor chip to the signal-connecting leads; and a resin encapsulant for encapsulating the die pad, the semiconductor chip, the signal-connecting leads and the connecting members. Respective lower parts of the die pad and the signal-connecting leads are at least partially not covered with the resin encapsulant but exposed. And the lower surface of the exposed part of the die pad is located at a level different from that of the lower surface of the exposed part of the signal-connecting leads.
When such a resin-molded semiconductor device is mounted onto a motherboard, the gap between the die pad and the motherboard is different in height from the gap between the signal-connecting leads and the motherboard. Accordingly, since the tension of solder interposed therebetween also differs between these two points, the device can be self-aligned more accurately and rapidly. That is to say, the time taken to realize good self-alignment can be shortened and the positional accuracy can also be improved.
In one embodiment of the present invention, the lower surface of the exposed part of the die pad is preferably located at a level lower than the lower surface of the exposed part of the signal-connecting leads.
In such a case, the level difference between the lower surfaces of the respective exposed parts of the die pad and the signal-connecting leads is preferably in the range from 10 xcexcm to 150 xcexcm.
In another embodiment, the respective lower parts of the die pad and the signal-connecting leads preferably both protrude at least partially from the resin encapsulant.
A fourth resin-molded semiconductor device according to the present invention includes: a semiconductor chip having electrode pads; a die pad for supporting the semiconductor chip thereon; support leads for supporting the die pad; signal-connecting leads; connecting members for electrically connecting the electrode pads of the semiconductor chip to the signal-connecting leads; and a resin encapsulant for encapsulating the die pad, the semiconductor chip, the signal-connecting leads and the connecting members. Respective lower parts of the die pad and the signal-connecting leads are at least partially not covered with the resin encapsulant but exposed. And each said support lead extends from an associated corner of the die pad to reach a side face of the resin encapsulant and is partially bent to function as a spring.
In this structure, during encapsulation using a lead frame where a die pad is located below an outer frame, clamping force, applied through a die assembly to the outer frame, can be transmitted to the die pad, while making the bent portions suppress the deformation of support leads. Thus, if encapsulation is performed with a seal tape adhered to the lower surface of the lead frame, then the die pad is forced into the seal tape. Accordingly, a structure in which the die pad protrudes downward from the back surface of the resin encapsulant can be obtained with more certainty. In addition, deformation of the die pad can be suppressed. As a result, the fifth object is accomplished while keeping the shape of the resin-molded semiconductor device good enough.
A fifth resin-molded semiconductor device according to the present invention includes: a semiconductor chip having electrode pads; a die pad for supporting the semiconductor chip thereon; support leads for supporting the die pad; signal-connecting leads; connecting members for electrically connecting the electrode pads of the semiconductor chip to the signal-connecting leads; and a resin encapsulant for encapsulating the die pad, the semiconductor chip, the signal-connecting leads and the connecting members. Respective lower parts of the die pad and the signal-connecting leads are at least partially not covered with the resin encapsulant but exposed. And the support leads are provided between the die pad and the signal-connecting leads.
When the chip and the lead frame are encapsulated with a resin encapsulant during the manufacturing process of the resin-molded semiconductor device having such a structure, clamping force, applied through a die assembly to the outer frame, can be transmitted to the die pad with more certainty. Accordingly, the same effects as those of the fourth resin-molded semiconductor device can be attained.
In one embodiment of the present invention, each said support lead is partially bent to function as a spring, and is partially cut off.
In such an embodiment, the signal-connecting leads, which was connected to the support leads, can be used for signal connection irrespective of the type of the semiconductor chip.
In another embodiment, a portion surrounding the cut part of each said support lead is thinner than the other parts of the support lead.
In such an embodiment, the support leads can be cut off more easily.
In still another embodiment, the lower surface of the exposed part of the die pad is preferably located at a level lower than the lower surface of the exposed part of the signal-connecting leads.
In the first to fifth resin-molded semiconductor devices, a groove portion is preferably formed in at least part of the signal-connecting leads.
In such a structure, even if the lower surface of the signal-connecting leads is not covered with the resin encapsulant but exposed, the resin encapsulant can hold the signal-connecting leads strongly enough.
A first method for manufacturing a resin-molded semiconductor device according to the present invention includes the steps of: a) preparing a lead frame, the lead frame including: an outer frame surrounding a region in which a semiconductor chip is mounted; a die pad for supporting the semiconductor chip thereon; support leads for connecting the die pad to the outer frame; and signal-connecting leads to be connected to the outer frame, the die pad being located below the signal-connecting leads; b) mounting the semiconductor chip, including electrode pads, onto the die pad; c) electrically connecting the electrode pads of the semiconductor chip to the signal-connecting leads with metal fine wires; d) attaching a seal tape to a die assembly while adhering the seal tape at least partially to the respective lower surfaces of the die pad and the signal-connecting leads of the lead frame; e) encapsulating the die pad, the semiconductor chip, the signal-connecting leads and the metal fine wires with a resin encapsulant; and f) removing the seal tape. The respective lower surfaces of the die pad and the signal-connecting leads are at least partially not covered with the back surface of the resin encapsulant but exposed. And the lower surface of the exposed part of the die pad is located at a level lower than the lower surface of the exposed part of the signal-connecting leads.
When a resin-molded semiconductor device is mounted onto a motherboard in accordance with this method, the large tension of solder or the like under the die pad regulates the self alignment of the device in terms of the position defined and the time taken. Accordingly, the device can be mounted at a desired position in a shorter time and with higher accuracy. That is to say, the third object is accomplished.
A second method for manufacturing a resin-molded semiconductor device according to the present invention includes the steps of: a) preparing a lead frame, the lead frame including: an outer frame surrounding a region in which a semiconductor chip is mounted; a die pad for supporting the semiconductor chip thereon; signal-connecting leads to be connected to the outer frame; and support leads interposed between the die pad and the signal-connecting leads; b) mounting the semiconductor chip, including electrode pads, onto the die pad; c) electrically connecting the electrode pads of the semiconductor chip to the signal-connecting leads with metal fine wires; d) attaching a seal tape to a die assembly while adhering the seal tape at least partially to the respective lower surfaces of the die pad and the signal-connecting leads of the lead frame; e) encapsulating the die pad, the semiconductor chip, the signal-connecting leads and the metal fine wires with a resin encapsulant; f) cutting off part of each said support lead; and g) removing the seal tape. The respective lower surfaces of the die pad and the signal-connecting leads are at least partially not covered with the back surface of the resin encapsulant but exposed.
In accordance with this method, clamping force, applied onto the outer frame of the lead frame, can be efficiently transmitted to the die pad through the support leads in the step e). Thus, a structure in which the die pad protrudes from the resin encapsulant can be obtained with more certainty. In addition, since the signal-connecting leads, which were connected to the support leads, are cut off from the die pad in the step f), the signal-connecting leads can be used for signal connection irrespective of the type of the semiconductor chip mounted. That is to say, the fifth object is accomplished.
In one embodiment of the first or second method according to the present invention, a metal plated layer may be formed on the surface of the lead frame in the step a).
In such an embodiment, plating work can be simplified as compared with a method in which only parts exposed out of a resin encapsulant are plated after the encapsulation. In addition, since the lead frame buried in the resin encapsulant is also plated, the reliability of the resin-molded semiconductor device improves.
In another embodiment of the first or second method, the thickness of the seal tape is adjusted in the step d) at a predetermined value such that at least part of the respective lower surfaces of the die pad and the signal-connecting leads protrude from the back surface of the resin encapsulant to reach respective desired heights.
In such an embodiment, the height of the part of the die pad protruding from the resin encapsulant can be adjusted at a desired value.
In still another embodiment of the first or second method, clearance grooves are formed in respective regions of the die assembly to make protruding portions of the die pad and the signal-connecting leads enter the grooves. And in the step e), encapsulation is performed while making at least part of the respective lower surfaces of the die pad and the signal-connecting leads enter the clearance grooves, thereby adjusting the respective heights of the portions protruding from the back surface of the resin encapsulant.
A third method for manufacturing a resin-molded semiconductor device according to the present invention includes the steps of: a) preparing a die assembly having a suction hole, a semiconductor chip and a peripheral member for the semiconductor chip; b) attaching a seal tape to between the peripheral member and the die assembly such that the seal tape adheres to part of a surface of the peripheral member; c) forming a hole in part of the seal tape adhered to the peripheral member; d) sucking part of the peripheral member through the suction hole of the die assembly and the hole of the tape; e) encapsulating the semiconductor chip and the peripheral member except for the part of the surface thereof in a resin encapsulant, with the seal tape adhered to the surface, and f) removing the seal tape after the step e) has been performed. After the step d) is finished, at least part of the surface of the peripheral member protrudes and is not covered with the resin encapsulant but exposed.
In accordance with this method, part of the peripheral member is forced into the seal tape as the member has been sucked through the suction hole of the die assembly in the step d). Accordingly, a resin-molded semiconductor device, in which part of the peripheral member protrudes from the resin encapsulant after the encapsulation, can be obtained. That is to say, the fifth object is accomplished.
In one embodiment of the present invention, a lead frame having a die pad may be prepared in the step a) as the peripheral member of the semiconductor chip, and the part of the surface of the peripheral member adhered to the tape in the step b) may be the die pad of the lead frame.
A fourth method for manufacturing a resin-molded semiconductor device according to the present invention includes the steps of: a) preparing a die assembly, a semiconductor chip and a peripheral member for the semiconductor chip; b) attaching a seal tape to between the peripheral member and the die assembly such that the seal tape adheres to part of a surface of the peripheral member, the thickness of the seal tape being in the range from 10 xcexcm to 150 xcexcm; c) encapsulating the semiconductor chip and the peripheral member except for at least the part of the surface thereof in a resin encapsulant, with the seal tape adhered to the surface, and d) removing the seal tape after the step c) has been performed. After the step d) is finished, at least part of the surface of the peripheral member protrudes and is not covered with the resin encapsulant but exposed.
In accordance with this method, a resin-molded semiconductor device, in which part of the peripheral member protrudes from the resin encapsulant after the encapsulation, is obtained. That is to say, the fifth object is accomplished.